Method for the continuous production of dropwise-irrigation tubes

ABSTRACT

In a method for the continuous manufacture of drip irrigation tubes which comprise a tube body ( 1 ) into which dosing elements are set ( 6 ), a hole is created in the walling of the tube body ( 1 ). This takes place by means of a laser beam ( 13 ) which is directed by an optical device ( 16 ). This optical device ( 16 ) has the effect of converting the laser beam ( 13 ) into the form of a ring, a line ( 19 ) of high energy density being formed corresponding substantially to the ring shape at a separation (a) from the optical device ( 16 ), whereby a particle ( 20 ) is cut from the walling.

[0001] This invention relates to a method for continuous manufacture ofdrip irrigation tubes according to the preamble of claim 1.

[0002] Drip irrigation tubes are used for direct irrigation of plants.For this purpose a dosing element is installed in this tube in thevicinity of each plant, through which dosing element the water is letout of the drip irrigation tube via a bore. Through this direct dripirrigation of the individual plants a large quantity of water is notwasted unnecessarily, as usually occurs with irrigation facilities inwhich water is distributed through spraying installations. With dripirrigation an extremely economical system is applied; the water can beused very sparingly.

[0003] The manufacture of drip irrigation tubes of this kind takes placein a known way through extrusion of a plastic material, the dosingelements being introduced with the desired spacing into the tube duringthe extruding. Then a hole must be made in the correct position in thewalling of the tube body allowing the drip discharge of the water.

[0004] Depending upon the application purpose, drip irrigation tubes ofdiffering design are used. For irrigation of plants which have to beplanted again every year, drip irrigation tubes are used having verythin walls and whose life is designed for a year. When replanting, newdrip irrigation tubes are installed on the surface. With perennial use,drip irrigation tubes are used whose life is correspondingly longer, andwhich are characterized by a larger wall thickness. These tubes canlikewise be installed on the surface; it is also conceivable, however,for them to be installed in the soil.

[0005] Known in the manufacture of these drip irrigation tubes is themaking of the holes by means of mechanical boring devices. This methodhas been shown to be relatively slow, however, which affects the costeffectiveness of the manufacturing method.

[0006] Known from EP 0 715 926 <U.S. Pat. No. 5,744,779> is a method formanufacturing drip irrigation tubes in which the holes are made by meansof a laser beam generated in a laser device. With this configuration,productivity can be greatly increased compared with the above-mentionedmethod using a mechanical boring device. The use of a laser of theNd/YAG type, however, only allows manufacture of drip irrigation tubeswith thin walling of maximally 0.6 mm since with thicker walling theenergy density of the laser beam would have to be increased so muchthat, in addition to the walling, the dosing element located underneathwould also be penetrated.

[0007] The object of the invention is therefore to create a method forcontinuous manufacture of drip irrigation tubes with which tubes havingthicker walls can also be produced at a high production rate and thuscost effectively.

[0008] This object is achieved according to the invention through thefeatures mentioned in claim 1.

[0009] Thus drip irrigation tubes can be manufactured in a productiveway whereby it is ensured that the hole in the walling is optimallydesigned without the material being damaged of the dosing element lyingunderneath, an optimal functioning of the drip irrigation tube therebybeing achieved.

[0010] In an advantageous way, the tube body of the drip irrigation tubeis directed during manufacture past the optical device in such a waythat the region in which the hole generated with the laser beam comes tolie has substantially the spacing a from the optical device, in whichregion the laser beam has a line with high energy density. It is therebyachieved that in an optimal way the particle is cut out of the walling,<and> at the same time the dosing element located underneath is notdamaged since in this area the energy density of the laser beam isalready considerably less again than at the height of the wall.

[0011] The directing of the tube body of the drip irrigation tube pastthe optical device takes place at substantially continuous rate of feed.Therefore the feed drive can be of simple construction; at the same timethe quality of the tube is ensured through the constant extrusion of thematerial.

[0012] In order to keep the measurements of the hole in the walling ofthe tube body as precise as possible, the optical device is preferablydesigned in such a way that the laser beam is directed along with theadvancing tube body during the making of the hole.

[0013] Preferably a CO₂ laser is used for the making of holes in thewalling of the tube body, by means of which optimal cutting features areachieved.

[0014] In order to fully exclude any damage to the dosing element duringthe making of the respective hole in the walling of the tube body, thisarea of the second chamber can be provided with a protective covering,consisting preferably of a metallic material, whereby the laser beamimpinging on this area is reflected for the most part.

[0015] A further preferred embodiment of the invention consists in thatthe particle cut out by the laser beam is suctioned with a suctiondevice, whereby this particle can be prevented from possibly being ableto end up in the second chamber and possibly being able to clog thehole.

[0016] The invention will be explained more closely in the followingwith reference to the attached drawing:

[0017]FIG. 1 shows in a schematic illustration the manufacture of thedrip irrigation tube;

[0018]FIG. 2 shows in section an enlarged detail of the walling of thetube body with inserted dosing element in which the effects are visiblewhen a conventional laser beam is used for making the hole:

[0019]FIG. 3 shows in a schematic illustration the course of the laserbeam for making the hole in the walling of the drip irrigation tube inthe method according to the invention; and

[0020]FIG. 4 shows a longitudinal section through the tube body in theregion of the inserted dosing element.

[0021] As can be seen from FIG. 1, the tube body 1 of the dripirrigation tube 2 is formed in a known way by an extrusion device 3 in acontinuous way. Inserted in this extruded tube body 1 is a dosingelement 6 in each case from a magazine 4 via a feed device 5, whichdosing element has a predetermined spacing from the preceding one. Theextruded tube body 1 with the inserted dosing elements 6 is thendirected through a calibration and cooling device 7 in which awatertight connection is obtained between tube body 1 and dosing element6, as will be described later.

[0022] The tube body 1 with the inserted dosing elements 6 is guided bya feed device 8 through a laser configuration 9, the rate of feed beingpreferably kept constant. In the laser configuration 9, the holepenetrating the walling of the tube body 1 is made by a laser beam.

[0023] Via a detector device 10, in a known way, it can be determined atwhich position the dosing elements 6 are disposed in the case of thetube body 1 passing through. This detector device 10 gives acorresponding signal to the control device 11, which is likewiseconnected to the feed device. Taking into consideration the rate of feedof the tube body 1 passing through, with a knowledge of the spacing ofthe detector device 10 from the laser beam in the laser configuration 9,this laser beam can be directed on the tube body 1 at the right moment,so that the hole penetrating the walling is made over the desired areaof the dosing element 6. The drip irrigation tube 2 thus produced can berolled up afterwards on a winding device 12, for example.

[0024] Now, when a hole is supposed to be made in a tube body 1 of adrip irrigation tube with a common Nd/YAG or CO₂ laser and the thicknessof the walling of the tube body 1 is more than one millimeter, forinstance, the situation arises as shown in FIG. 2. The laser beam 13hits the walling of the tube body 1. Since the laser beam 13 has thegreatest energy density in its central region 14, the material of thewalling of the tube body 1 is first burned, or respectively volatized,in this central region 14. A first penetration of the material of thewalling of the tube body 1 thus takes place in this central region 14.Afterwards the hole 15 thus formed is extended in diameter; in themeantime, however, the high energy central region 14 of the laser beam13 already reaches the material of the dosing element 6 located behindthe walling of the tube body 1. The material is destroyed. Before thedesired diameter of the hole 15 is achieved, a penetration of the dosingelement 6 can take place, which is absolutely undesired, since thedosing element 6 can then no longer fulfil its function.

[0025] As can be seen from FIG. 3, an optical device 16 is disposed inthe laser configuration 9 as used in the device according to FIG. 1.This optical device 16 comprises a system of lenses (e.g. an axicon),the lenses being shown only schematically. The laser beam 13 is ledthrough this optical device 16 or respectively through the system oflenses 17. The laser beam 13 is converted here into a ring form 18. Therays are “bundled” here in such a way that quasi a line 19 (focal line)comes into being in the region where the energy density is high.

[0026] The tube body 1 is now directed past the optical device 16 insuch a way that the walling of the tube body 1, in which the holegenerated by the laser beam 13 comes to lie in each case, has thespacing a from this optical device 16. The ring form 18 of the laserbeam 13 then cuts a particle 20 out of the walling of this tube body 1,which particle is suctioned up by a suction device (not shown) disposedimmediately next to the “cutting device.”

[0027] The cutting of the particle 20 out of the walling of the tubebody 1 takes place over the entire circumference at the same time. Assoon as the particle 20 is cut out, the laser processing can thereforebe ended immediately. The beam, still reaching the material of thedosing element 6 after the cutting out of the particle, thus practicallydoes not damage the material here at all, on the one hand owing to thevery short duration, on the other hand also because the energy densityof the beam in this area is already considerably less than in the regionof the line 19 since the beam is already “scattered” again.

[0028] To prevent any damage to the material of the dosing element 6 inthe region of the laser processing, a protective covering 21 can beused, which consists, for example, of aluminum or of another metallicmaterial. This protective covering 21 reflects for the most part theimpinging laser beam.

[0029] So that the making of the holes can take place at the greatestpossible, and substantially constant, speed, the optical device isdesigned in such a way that the laser beam is directed along with theadvancing tube body 1 during the cutting out of the particle 20. Thiscan be achieved in a known way (not shown) through pivoting of theoptical device 16; this can also be achieved by using a pivotablemirror, it being possible for the control of these movements to takeplace by means of the control device 11 (FIG. 1). In this way thecontour of the hole will also be optimal. With this procedure dripirrigation tubes can be manufactured at high rate of production having,for instance, a diameter of about 10 to 30 mm and a wall thickness ofabout 0.6 to 3 mm.

[0030] The ring form 18 of the laser beam is preferably circular. Otherring shapes are also conceivable, however, which can be formed viasuitable optics.

[0031] Shown in FIG. 4 is a detail of a drip irrigation tube 2 insection, in which the dosing element 6 is designed as a hollow cylinder.As already mentioned, this dosing element 6 is used in the extrusionprocess for production of the tube body 1. In the calibrating andcooling device 7 (FIG. 1), the tube body 1 places itself on the outsideof the dosing element 6 in an absolutely watertight way.

[0032] The dosing element 6 shown here has a first chamber 22 which isconnected, via at least one opening 23, to the internal space of thedosing element 6, or respectively the tube body 1. The water led inthrough the drip irrigation tube 2 arrives via this opening 23 in thefirst chamber 22 of the dosing element 6, which chamber is of annulardesign. A second chamber 24 is disposed in the dosing element 6 spacedapart from the first chamber 22. This second chamber 24 is also ofannular design in the present embodiment example. As has been describedin the foregoing, the hole is made in the region of this second chamber24 by means of laser. In a known way, a labyrinth configuration (notshown) is disposed between the first chamber 22 and the second chamber24 in the dosing element 6. Thus the water comes out of the internalspace of the tube body 1 via the opening 23 into the first chamber 22and via the labyrinth configuration into the second chamber 24, out ofwhich chamber it can emerge via the holes 15 and can supply the plantswith water. Owing to the labyrinth configuration, the water escapesthrough the hole only drop by drop. The number of drops per unit of timewhich escape through the hole 15 results from the choice of labyrinthconfiguration and the measurements of the holes 15.

[0033] It can be seen in this FIG. 4 that the protective covering 21with which the floor of the second chamber 24 is provided, in order toprevent damage to the dosing element 6 during the laser processing, hasthe shape of a ring. The protective covering 21 could also be obtained,however, through vacuum deposition of a metal layer on the correspondingarea of the dosing element 6.

[0034] Of course the dosing element 6 does not have to be of hollowcylindrical shape, as described in the foregoing. Use of a flat part asthe dosing element is also conceivable, which part is stuck into thetube body during the extrusion process for producing the latter, as isshown, for example, in the previously described EP-A-0 715 926 <U.S.Pat. No. 5,744,779>.

[0035] Polyethylene is suitable as a material for the tube body 1 of thedrip irrigation tube 2. The dosing elements can also be made of thismaterial. Other materials can certainly also be used, however, whichfulfil the desired prerequisites.

1. A method for continuous manufacture of drip irrigation tubes (2), thetube bodies (1) of which are obtained by means of an extrusion step fora plastic, in which tube bodies dosing elements (6) are set during theextrusion step with a spacing from one another which dosing elementseach have a first chamber connected to the interior space of the tubebody (1), which first chamber is connected via a labyrinth to a secondchamber (24) provided in the respective dosing element (6), which secondchamber is disposed in a sealing way on the inner surface of the tubebody (1), and in which tube bodies (1) at least one hole (15)penetrating the walling is made in the area of the second chamber (24)of the respective dosing element (6) with a laser beam (13) generated ina laser configuration (9), wherein an optical device (16) is used bymeans of which a laser beam (13) is directed, and whereby it is achievedthat the laser beam (13) is converted into the form of a ring, a line(19) of high energy density being formed corresponding substantially tothe ring shape at a separation (a) from the optical device (16), wherebya particle (20) is cut from the walling.
 2. The method according toclaim 1, wherein the tube body (1) of the drip irrigation tube (2) isdirected past the optical device (16) in such a way that the region inwhich the hole (15) generated with the laser beam (13) comes to lie ineach case has substantially the spacing (a) from the optical device(16).
 3. The method according to claim 1 or 2, wherein the directing ofthe tube body (1) of the drip irrigation tube (2) past the opticaldevice (16) is undertaken with substantially constant rate of feed. 4.The method according to claim 3, wherein the optical device (16) isdesigned in such a way that the laser beam (13) is directed along withthe advancing tube body (1) during the making of the hole (15).
 5. Themethod according to one of the claims 1 to 4, wherein a CO₂ laser isused for the making of holes (15) in the walling of the tube body (1).6. The method according to one of the claims 1 to 5, wherein the floorof the second chamber (24) is provided with a protective covering (21)at least in the region of each hole (15) able to be made in the wallingof the tube body (1).
 7. The method according to one of the claims 1 to6, wherein the particle (20) cut out by the laser beam (13) is suctionedwith a suction device.
 8. The method according to one of the claims 1 to7, wherein the tube body (1) is made of polyethylene.